PID

**Note:** "PID" has other meanings. These include primary immunodeficiency, prolapsed intervertebral disc, and proportional-integral-derivative. This entry covers pelvic inflammatory disease, which is the usual meaning on USMLE.

**Pathophysiology** - Organisms ascend from the cervix or vagina into the endometrium, fallopian tubes, ovaries, and peritoneum. - Main pathogens: *Chlamydia trachomatis* (most common) and *Neisseria gonorrhoeae*. Infection is often polymicrobial, with anaerobes (as in bacterial vaginosis), *Gardnerella*, *Haemophilus influenzae*, enteric gram-negatives, and *Mycoplasma genitalium*. - Risk factors: age 15–25, multiple or new partners, prior STI or PID, no barrier contraception, and recent IUD insertion (the risk is mainly in the first 3 weeks). Instrumentation that breaches the cervical barrier, such as D&C or hysteroscopy, also raises risk. - Chlamydia is often asymptomatic. Silent infection leads to tubal scarring.

**Clinical features** - Lower abdominal or pelvic pain (the hallmark), abnormal vaginal discharge, abnormal uterine bleeding, dyspareunia, and fever. - Exam findings: cervical motion tenderness ("chandelier sign"), uterine tenderness, and adnexal tenderness. Mucopurulent cervicitis is also common. - **Fitz-Hugh–Curtis syndrome:** perihepatitis with RUQ pain and "violin-string" adhesions between the liver capsule and the diaphragm or abdominal wall. LFTs are usually normal. It is seen with chlamydia and gonorrhea.

**Diagnosis** - This is a clinical diagnosis. CDC guidance says to treat empirically in a sexually active woman with pelvic or lower abdominal pain if there is cervical motion, uterine, or adnexal tenderness and no other cause is found. - Supportive findings: fever >38.3°C, mucopurulent discharge, WBCs on wet mount, elevated ESR or CRP, and a positive NAAT for chlamydia or gonorrhea. - Always get a **pregnancy test** to exclude ectopic pregnancy. - Pelvic ultrasound is used if an abscess is suspected. It shows a tubo-ovarian abscess or hydrosalpinx. - Laparoscopy is the gold standard but is rarely needed.

**Treatment** - **Outpatient (mild to moderate):** ceftriaxone IM once, plus doxycycline PO for 14 days, plus metronidazole PO for 14 days. - **Inpatient (severe, pregnant, tubo-ovarian abscess, unable to tolerate oral therapy, or failed outpatient therapy):** IV cefoxitin or cefotetan plus doxycycline. Clindamycin plus gentamicin is an alternative. - Treat sexual partners. An IUD generally does not need to be removed. - A tubo-ovarian abscess that does not respond to antibiotics needs drainage. A ruptured abscess is a surgical emergency.

**Complications** - Infertility from tubal scarring. The risk increases with each episode. - Ectopic pregnancy, from damaged tubal cilia and scarring. - Chronic pelvic pain. - Tubo-ovarian abscess. - Hydrosalpinx. - Peritonitis and sepsis. - Fitz-Hugh–Curtis syndrome.

**High-yield associations and pearls** - A young woman with pelvic pain, fever, and cervical motion tenderness has PID until proven otherwise. Rule out ectopic pregnancy first. - Gonorrhea is a gram-negative diplococcus and is treated with ceftriaxone. Chlamydia is an obligate intracellular organism and is treated with doxycycline (or azithromycin). - Differential: ectopic pregnancy, appendicitis, ovarian torsion, endometriosis, and ruptured ovarian cyst.